`a) x^6 - 105x^5 + 105x^4 - 105x^3 + 105x^2 + 105x + 105`
`= x^6 - (104 + 1)x^5 + (104 + 1)x^4 - (104 + 1)x^3 + (104 + 1)x^2 + (104 + 1)x + 105`
`= x^6 - (x + 1)x^5 + (x + 1)x^4 - (x + 1)x^3 + (x + 1)x^2 + (x + 1)x + 105`
`= x^6 - x^6 + x^5 + x^5 + x^4 - x^4 - x^3 + x^3 + x^2 + x^2 + x + 105`
`= 2x^2 + x + 105`
`= 2. 104^2 + 104 + 105`
`= 21841`
`b) 5431. 5432 - 5430. 5433`
`= (5430 + 1). (5433 - 1) - 5430. 5433`
`= 5430. 5433 - 5430 + 5433 - 1 - 5430. 5433`
`= (5430. 5433 - 5430. 5433) + (-5430 + 5433 - 1)`
`= 0 + 2`
`= 2`